THE SQUARE CAMPAIGN: Ladder-campaign adjacent rules for a limited duration, thematically coherent four-player wargame campaign
Here's a system I used to play a GMless Warhammer Fantasy Battles (8th ed) campaign in 2023. I quite like it, and I think it'd be useful for others too. It has the advantages of not requiring a GM and reflecting the progress of each army whilst still producing thematically coherent outcomes. It's not going to be as in-depth as a GMed map campaign probably, and it needs exactly four fairly committed players (well, I'm sure you could make a triangle or hex variant tbf), but what can you do? Although built around Warhammer, it should be workable for any wargame that uses points and has scenarios - you may just need to find a suitable way to replicate the massacre/major victory/minor victory/draw distinction WHFB makes. My experience has been that it's played pretty quickly and produced plausible, fun results. (Rules which didn't do this were smoothed out over time). There's a bit of a death-spiral, but it's not so quick that people can't make a comeback...